Wind tunnel investigations of supersonic transport configurations having highly swept arrow wings indicate that high levels of aerodynamic efficiency can be obtained at Mach numbers on the order of 2.7. Furthermore, the investigations indicate that minimum trim drag at supersonic speeds can be obtained by positioning the aircraft center-of-gravity relatively far aft.
However, such configurations exhibit relatively poor low-speed characteristics. In particular, the highly-swept arrow wing configuration exhibits a comparatively shallow lift-curve slope which, when coupled with the aircraft tail scrape angle, limits take-off lift coefficients to values of approximately 0.55. Furthermore, for this take-off lift coefficient of 0.55 to be achieved, a fairly high angle of attack is necessary which constrains airframe design to inclusion of both a "visor"-type nose, to provide acceptable pilot visibility, and an elongated landing gear installation to maximize tail scrape angle. Moreover, this high angle of attack results in a significant increase in drag imposing penalties on low-speed performance.
The most significant penalty involves the take-off field length constraint. In order to provide acceptable take-off field lengths, the conventional highly-swept arrow wing configuration requires a wing area and installed thrust substantially above that required to provide efficient supersonic cruise. As a consequence, aircraft range is forfeited.
The second problem, encountered in the low-speed flight regime, is the nonlinear variation of pitching moment with respect to angle of attack. There is a tendency for the aircraft to pitch up due to the formation of vortices at the wing apex as the aircraft angle of attack is increased.
The third significant problem associated with such configurations is the forward shift in aerodynamic center as the aircraft speed goes from supersonic to subsonic. Where the aircraft center-of-gravity is positioned to provide minimum trim drag at design Mach numbers of approximately 2.7, the shift in aerodynamic center to a more forward position at low speeds induces longitudinal instability.
It is therefore an object of the present invention to increase take-off lift at a reduced angle of attack.
Another object of the present invention is to apply thrust vectoring concepts to increase take-off lift.
A further object of the invention is to offset the pitching moment induced by thrust vectoring.
An additional object is to eliminate the nonlinear variation in pitching moment as related to angle of attack.
A further additional object is to restrain the formation of wing apex vortices which cause nonlinear variations in pitching moment with respect to aircraft angle of attack.
Another additional object is to provide longitudinal stability at low speeds.
A still further object is to provide canard surfaces for low speed longitudinal stability while maintaining an aircraft configuration providing efficient supersonic cruise.